/Engine/Source/Runtime/Engine/Classes/Engine/World.h
Associates the passed in level with the world. The work to make the level visible is spread across several frames and this function has to be called till it returns true for the level to be visible/ associated with the world and no longer be in a limbo state.
void AddToWorld ( [ULevel](API\Runtime\Engine\Engine\ULevel) * Level, const FTransform & LevelTransform, bool bConsiderTimeLimit, [FNetLevelVisibilityTransactionId](API\Runtime\Engine\GameFramework\FNetLevelVisibilityTransactionId) TransactionId, [ULevelStreaming](API\Runtime\Engine\Engine\ULevelStreaming) * OwningLevelStreaming )